Nanoindenter
A new type of indenter is described. This device combines certain sensing and structural elements of atomic force microscopy with a module designed for the use of indentation probes, conventional diamond and otherwise, as well as unconventional designs, to produce high resolution and otherwise superior indentation measurements.
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An AFM is a device used to produce images of surface topography (and other sample characteristics) based on information obtained from rastering a sharp probe on the end of a cantilever relative to the surface of the sample. Deflections of the cantilever, or changes in its oscillation, which are detected while rastering correspond to topographical (or other) features of the sample. Deflections or changes in oscillation are typically detected by an optical lever arrangement whereby a light beam is directed onto a cantilever in the same reference frame as the optical lever. The beam reflected from the cantilever is made to illuminate a position sensitive detector (PSD). As the deflection or oscillation of the cantilever changes, the position of the reflected spot on the PSD changes, causing a change in the output from the PSD. Changes in the deflection or oscillation of the cantilever are typically made to trigger a change in the vertical position of the cantilever base relative to the sample, in order to maintain the deflection or oscillation at a constant pre-set value. It is this feedback that generates an AFM image. AFMs can be operated in a number of different imaging modes, including contact mode where the tip of the cantilever is in constant contact with the sample surface, and oscillatory modes where the tip makes no contact or only intermittent contact with the surface.
Actuators are commonly used in AFMs, for example to raster the probe relative to the sample surface or to change the position of the cantilever base relative to the sample surface. The purpose of actuators is to provide relative movement between the probe and the sample. For different purposes and different results, it may be useful to actuate the sample, or the tip or some combination of both. Sensors are also commonly used in AFMs. They are used to detect movement of various components of the AFM, including movement created by actuators. For the purposes of the specification, unless otherwise specified, the term “actuator” refers to a broad array of devices that convert input signals into physical motion, including piezo activated flexures, piezo tubes, piezo stacks, blocks, bimorphs, unimorphs, linear motors, electrostrictive actuators, electrostatic motors, capacitive motors, voice coil actuators and magnetostrictive actuators, and the term “position sensor” or “sensor” refers to a device that converts a displacement, velocity or acceleration into an electrical signal, including capacitive sensors, inductive sensors (including eddy current sensors), differential transformers (such as described in co-pending applications US20020175677A1 and US20040075428A1,Linear Variable Differential Transformers for High Precision Position Measurements, and US20040056653A1, Linear Variable Differential Transformer with Digital Electronics, which are hereby incorporated by reference in their entirety), variable inductance, optical interferometry, optical deflection detectors (including those referred to above as a PSD and those described in co-pending applications US20030209060A1 and US20040079142A1, Apparatus and Method for Isolating and Measuring Movement in Metrology Apparatus, which are hereby incorporated by reference in their entirety), strain gages, piezo sensors, magnetostrictive and electrostrictive sensors.
SUMMARY OF THE INVENTIONWe have developed a nanoindenter that produces very accurate, quantitative characterization for a wide spectrum of materials. The new nanoindenter may be implemented on an atomic force microscope (AFM) platform, but unlike indentation that might be effected with an AFM cantilever, the invention drives the indenting tip perpendicularly into the sample. Displacement and force are measured with optimized LVDT sensors and an Optical Lever, respectively, the same devices that eliminate inaccuracies (e.g. non linearity) present in measurements made with AFMs, and this greatly increases sensitivity and resolution in comparison to commercial indenters. This highly quantitative tool, incorporating high end AFM capabilities breaks new ground in characterization of a great diversity of materials including thin films, coatings, polymers, etc. As noted, the nanoindenter may be implemented on an AFM platform and when integrated with the native metrology abilities of the Molecular Force Probe-3D AFM of Asylum Research Corporation, it enables the user to perform quantitative indentation measurements and to make quantitative statements regarding the indenter tip shape and indentation volumes and profiles, all with the same instrument set-up.
In addition to an AFM platform, the new nanoindenter may be implemented on other cantilever-based instruments. Cantilever-based instruments include such instruments as AFMs, molecular force probe instruments (1 D or 3D), high-resolution profilometers and chemical or biological sensing probes. For the sake of convenience, the specification focuses on AFMs. However, it should be understood that problems addressed and solutions presented by the present invention are also applicable to other instruments with nanoscale motion and metrology applications.
The systems and techniques described herein provide a novel device for nanoscale metrology that permits quantitative measurements of indentation and related parameters better than is presently possible with commercially available tools.
Specifics of the invention will be described in greater detail below.
One preferred embodiment of the current invention is depicted in
Another useful feature of the indenter module 12 being installed in the MFP-3D head 13 is that the module can use certain optical features of the head for providing an optical view of the indenter probe 303 and the sample. The top-view objective 18 and steering minor 19 of the MFP-3D head 13 work with the prism of the indenter module 12 to provide an optical view of both the indenter probe 303 and the sample (not shown), as well as to illuminate both. This is of great utility for aligning the indenter probe 303 with particular structures on the sample.
The indenter can similarly be installed in AFMs manufactured by other companies and, with modifications, in yet other AFMs. The MFP-3D of Asylum Research Corporation is particularly amenable to conversion to an indenter because the actuators, sensors and optics located in its head are appropriate and convenient for indenter purposes. The same is true of other AFMs, or could be made to be true with modifications.
Except where clearly stated otherwise, the remainder of this Detailed Discussion of the current invention is directed at an indenter module that might be installed in any AFM, not just the MFP-3D of Asylum Research Corporation, as well as to a stand-alone indenter that is not a component of an AFM.
As shown in
The design of the mechanical converter assembly allows the motion of the indenter tip 303 to be measured in much the same manner as cantilever tip deflection or oscillation are measured in a conventional AFM. Together with the use of the z-axis actuator previously discussed, this allows the indenter module to be easily swapped with the cantilever holder of an AFM, resulting in a unique, useful and versatile instrument that allows the user to bring the functionality of an AFM to bear on indenting.
The planar flexure 314 has a very high compliance when compared to the indenting flexure 305, that is, the spring constant of the planar flexure 314 is very low compared to the spring constant of the indenting flexure 305.
It will be observed that the indenting flexure 305 plays a major role in the performance of the preferred embodiment of the current invention which has just been discussed. A second preferred embodiment, employing a different indenting flexure but, like the first preferred embodiment, designed to be installed in an AFM in place of the cantilever holder in order to make use of the actuators, sensors and optics of the AFM is depicted in
Unlike the monolithic three-dimensional leaf spring flexure 305 of the first preferred embodiment, the flexure of
As with the first preferred embodiment, the central shaft of the assembled flexure of
Other preferred embodiments of the current invention, also designed to be installed in an AFM in place of the cantilever holder in order to make use of the actuators, sensors and optics of the AFM, but employing a different indenting flexures than indenting flexure 305 of the first preferred embodiment or the assembled flexure of
An additional preferred embodiment, again employing a different indenting flexure but, like the other preferred embodiments disclosed above, designed to be installed in an AFM in place of the cantilever holder in order to make use of the actuators, sensors and optics of the AFM is depicted in
The components of the assembled flexure of
The central shaft of the planar leaf springs 707 and 708 of the assembled flexure of
The probe 703 of the assembled flexure of
Probe 703 has many advantages over other indenter transducers or indenting probes. These include making available true top optical view of the sample to be indented, allowing for accurate positioning of indentations and having a combination of low mass and high resonant frequency, which allows unprecedented resolution in the measurement of mechanical behavior of materials through both static and dynamic material testing methods.
The described embodiments of the invention are only considered to be preferred and illustrative of the inventive concept. The scope of the invention is not to be restricted to such embodiments. Various and numerous other arrangements may be devised by one skilled in the art without departing from the spirit and scope of the invention.
Claims
1. An assembly, comprising: an indenter portion, including an indenter probe; an actuator, operating to move the indenter probe perpendicularly relative to a sample; detection devices including a first portion operating to detect displacement imparted by said actuator and a second portion operating to detect displacement of said indenter probe; wherein a force applied by said indenter probe is detected by said detection devices; an optical system which allows direct optical view of a sample to which force is applied.
2. The assembly as in claim 1, wherein said indenter portion forms a module which is installed in a cantilever based instrument in place of a cantilever holder and uses the optics, actuators and sensors of said cantilever based instrument.
3. The assembly as in claim 1, wherein said indenter portion includes a three-dimensional flexure through which the indenter probe is moved by an actuator in a Z axis direction.
4. The assembly as in claim 3 wherein said flexure has first, second and third portions which constrain the flexure against movement in directions other than said Z axis direction and a flexing portion at a center portion thereof.
5. An assembly as in claim 4 wherein said three portions of said flexure have supporting portions at outer edges thereof.
6. An assembly as in claim 3, further comprising hard stops that prevent extending the flexure in said Z axis direction by more than a specified amount.
7. An assembly, comprising:
- a measuring instrument which includes a connection to a measuring part, an actuator for said measuring part, and sensors for measuring displacement and force of said measuring part, where said measuring part is adapted to connect to an optical lever that has a lever that moves non-perpendicular to a measured sample; and
- an indenter portion, including an indenter probe, said indenter portion being movable to move perpendicularly relative to a sample being measured, and connects to said connection and uses the same actuator and sensors as said measuring part,
- wherein said indenter portion includes a three-dimensional flexure through which the indenter probe is moved by said actuator in a Z axis direction, which is a direction perpendicular to a plane of the flexure and perpendicular to the sample.
8. An assembly as in claim 7, wherein said measuring instrument is an atomic force microscope.
9. An assembly, comprising:
- a measuring instrument which includes a connection to a cantilever, an actuator for said cantilever portion, and sensors for measuring displacement and force of said cantilever portion; and
- an indenter portion, including an indenter probe, said indenter portion being movable to move perpendicularly relative to a sample being measured, wherein said indenter probe uses the same actuator and sensors as said instrument, and wherein said indenter portion includes a three-dimensional flexure through which the indenter probe is moved by said actuator in a Z axis direction, which is a direction perpendicular to a plane of the flexure and perpendicular to the sample.
10. An assembly as in claim 9, further comprising a cover which constrains movement of said flexure beyond a specified amount.
11. An assembly as in claim 9, wherein said flexure has first, second and third portions which constrain the flexure against movement in directions other than said Z axis direction and a flexing portion at a center portion thereof.
12. An assembly as in claim 11, wherein said flexure is a three-dimensional leaf spring.
13. An assembly as in claim 11, wherein said three portions of said three-dimensional leaf spring have supporting portions at outer edges thereof.
14. An assembly as in claim 9, further comprising a structure that converts linear motion of the indenter probe into angular motion of a type that is monitored by sensors of the cantilever portion.
15. An assembly as in claim 10 wherein said cover includes hard stops that prevent extending the flexure in said Z axis direction by more than a specified amount.
16. An assembly, comprising:
- a measuring instrument which includes a connection to a cantilever, an actuator for said cantilever portion, and sensors for measuring displacement and force of said cantilever portion; and
- an indenter portion, including an indenter probe, said indenter portion being movable to move perpendicularly relative to a sample being measured, wherein said indenter probe uses the same actuator and sensors as said instrument wherein said indenter portion forms a module which is installed in said instrument in place of a cantilever holder, wherein said indenter portion includes a three-dimensional flexure having a circular outer shape through which the indenter probe is moved by said actuator in a Z axis direction.
17. An assembly as in claim 16, wherein said flexure includes a spring, which is formed of first spring and second spring portions, said spring portion being interleaved with a clamp constraining the spring at its periphery which is formed of a first clamp portion, a second clamp portion and a third clamp portion, and a flexing portion at a center portion thereof.
18. An assembly as in claim 16, wherein said spring is a planar leaf spring.
19. An assembly, comprising:
- a measuring instrument which includes a connection to a cantilever, an actuator for said cantilever portion, and sensors for measuring displacement and force of said cantilever portion;
- an indenter portion, including an indenter probe, said indenter portion being movable to move perpendicularly relative to a sample being measured, wherein said indenter probe uses the same actuator and sensors as said instrument; and
- an angular change element, that detects linear changes in the indenter probe and converts such changes into angular changes which are detected by the sensors of said cantilever portion.
20. An assembly as in claim 19, wherein said measuring instrument also uses optics for obtaining information from movement of the cantilever, and wherein said indenter portion uses the same said optics as said measuring instrument.
Type: Application
Filed: Jun 12, 2012
Publication Date: Oct 25, 2012
Patent Grant number: 9063042
Applicant: ASYLUM RESEARCH CORPORATION (Goleta, CA)
Inventors: Flavio Alejandro Bonilla (Santa Barbara, CA), Roger Proksch (Santa Barbara, CA), Jason Cleveland (Ventura, CA), Tim Sauter (Santa Barbara, CA)
Application Number: 13/494,526
International Classification: G01Q 20/02 (20100101);